Wear of ceramic coated metal-on-metal bearings used for hip replacement

Abstract

This work consists of a preliminary evaluation of the performance of TiN, TiNbN and TiCN thin coatings to improve the tribological behaviour of stainless steel (SS) metal-on-metal prostheses. Coatings of TiN, TiNbN and TiCN, with a thickness between 2 and 5 μm, were applied by physical vapour deposition (PVD) on AISI 316L stainless steel substrates. The hardness of TiNbN and TiCN is similar and considerably higher than that of TiN which, in turn, is much higher than that of the SS. Topographical analysis, carried out by atomic force microscopy (AFM), showed that PVD leads to the formation of very smooth coatings, with their average roughness ( R a) between 37 and 44 nm. Ball-on-disk short-term tests were done using Hanks’ balanced salt solution as lubricant. When both rubbing surfaces were coated, the best results were obtained with TiCN and TiN coatings. Tests of the bare SS balls against the coated disks indicated TiN as the most efficient coating. The worn surfaces were observed by scanning electron microscopy (SEM), which enabled for the identification of the wear mechanisms operating in each tribological pair.